Telephone system



Sept 10, 1940- E. s. PETERSON TELEPHONE SYSTEM Filed Oct. 5. 1938 8 Sheets-Shea?l l Sept. 10, 1940.

E.' S. PETERSON TELEPHONE SYSTEM Filed om.. s, 193s a sheets-sheet 2 www @PRQQ INVENTOR. Edward 5. Feler'snn BY/mzw,

m FL

ATTORNEYS.

E. s. PETERsoN 2,214,256

TELEPHONE SYSTEM Filed Oct. 5.` 1938 8 Sheets-Sheet 3 Sept. l0, 1940.

Sept. l0, 1946. E. s. PETERSON 2,214,256

TELEPHONE SYSTEM Filed Oct. 5, 1938 8 Sheets-Sheet 4 Sept. 10, 1940, E. s. PETERSON TELEPHONE SYSTEM Filed Oct. 3, 1938 8: Sheets-Sheet 5 MSG Filedpct. 3, 193e 8 sheets-sheet e INVENTOR. Edward E. FaTsrsun ,MQ/,M #40,125

ATTORNEY 5.

Sept. l0, 1940. E. s. PETERSON TELEPHONE SYSTEM Filed Oct. 3, 1938 8 Sheets-Sheet 7 Sept. 10, 1940. E. s. PETERSON TELEPHONE SYSTEM 8 Sheets-Sheet 8 Filed Oct. 3, 1958 @In mwhm, QR

INVENTOR. Edward. E FeTl-'snn ATTORNEYS.

emma sept- 1o, 1940 UNITED STATES- TELEPHONE srs'rii'Ml Edward Sigtord Peterson signor to Associated El Elmwood Park, lll.,v asectric Laboratories, Inc.,

Chicago, Ill., a corporation of Delaware v Application October 3, 1938, Serial No. 233,021

1s claims. (ci. 17e- 16) 'Ihe present invention relates to telephone systems and more particularly to telephone systems comprising a number of interconnected exchanges of the automatic type.

In a telephone system comprising a number of interconnected automatic exchanges, each exchange usually includes a plurality of automatic switching links having access to the subscriber lines terminating at the exchange and to the trunk lines extending between the exchanges for setting up connections between the various lines, and a distributor for assigning idle ones of the links to the use of calling ones of the lines in a predetermined order. Frequently, some of the subscriber lines terminating at each of the exchanges are of theA multiparty type; and each of the links in the exchange is provided with a switch operative to select characteristic sources of ringing current to be projected over the called subscriber lines of the multiparty type selected by the link. v

An alternating current repeater is frequently associated with each trunk line terminating at each exchange, wherebyl a connection between two of the subscriber lines respectively terminating in two of the exchanges is set up therebetween by way of one of the trunk lines extending between the exchanges and the repeaters associated with the one trunk line in the exchanges. In-setting up a connection between two of the subscriber lines respectively terminating at two of the exchanges, when repeaters of this character are utilized, a repeater in the calling exchange associated with an idle trunk line extending between the exchanges is controlled in accordance with switch control impulses transmitted thereto from one of the links in the calling exchange which has seized a calling line and Y is operative to transmit alternating current impulses over the trunk line to the called exchange. 'Ihe repeater associated with the trunk line in the call-edexchange is operative in response to the alternating current impulses transmitted thereto to transmit switch control impulses therefrom to an idle link in the called exchange, thereby to cause the link to seize the called line. Usually the release of this connection is primarily under the control of the calling line, in which event Y the calling line must be released in order to cause the link seizing it to be released, whereupon the associated repeater in the calling exchange associated with the trunk line is released, whereby alternating current release impulses are transmitted from the repeater in the calling exchange over the trunk line to the called exchange. The

` cally operative to force the release of the aprepeater associated with the trunk line in the called exchange is released in response to the alternating current release impulses transmitted thereto, thereby to cause the associated link to be released in order to release the called line. From 5 the foregoing it will be apparent that this connection must be released in a particular manner, and under the control' of the calling line, in order to insure that all of the apparatus utilized in setting up this connection is properly `10 released for further use.

It is noted that it is desirable that an established connection between any two of the lines in the system, whether the lines terminate in the same or different exchanges, be held only a prel5 determined time interval, thereby to restrict the use of an established connection toa reasonable time interval in order'to minimize the amount of apparatus required in each of the exchanges and the number of trunk lines extending there- 20 between. Accordingly, it is desirable that automatic timing means be provided in the system in order eiect this end. A timing means of this character may be provided which is automati- 25 paratus utilized in establishing a connection between two `lines terminating in the same exchange, in order to eiectively clear out the connection'. However, such a timing means would not be eiective to clear out a. connection established between two lines `terminating in different exchanges due to the fact that the apparatus utilized in the established connection includes an alternating current repeater in each of the exchanges associated with the trunk line, which 35 repeaters must be released under the control of the calling line, as previously explained.

Accordingly, it is an object of the present invention to provide in a telephone system comprising a number of interconnected automatic exchanges and apparatus for setting up connections between lthe exchanges; an improved arrangement for eiecting the release of an established connection set up between the exchanges a predetermined time interval after the connection is set up.

Another object of the invention is to provide, in a telephone system of the character described comprising. a number of interconnected automatic exchanges, each terminating a number of 50 subscriber lines having subscriber substations associated therewith, and apparatus for setting up connections between the substations; an automatic arrangement for giving a warning to the subscribers at two ofthe substations respectively 55 associated with two of the lines respectively terminating at two of the exchanges and involved in an established communication connection set up therebetween a first predetermined time interval after the connection is set up and then for blocking the communication connection a second predetermined time interval after the connection is set up.

The features of the invention are illustrated as being incorporated in a telephone system including an automatic central office or exchange and an automatic suboilice or Subexchange interconnected by a plurality of trunk lines, an alter- `nating current repeater in each of the oilces being associated with each of the trunk lines terminating thereat. Also, a number of subscriber linesfsome of which are of the multipartytype, are terminated'in each of the ofiices; and each office includes a number of switching links having access to the subscriber lines terminating thereat and to the repeater therein for setting up connections between the various lines, and a distributor for assigning idle ones of the links therein to the use of calling ones of the lines terminating thereat in a predetermined order. Each of the links, in at least the suboflice, comprises timing means including a stepping switch which is initially operative to select one of a number of characteristic sources of ringing current to be projected over a called line terminating at the suboiiice and selected by the link, and which is subsequently operative after a iirst time interval to cause warning current to be applied to an established connection set up between two of the subscriber lines terminating at the suboflice by way of the link, and which is finally operative after a second time interval to cause the vlink to be released. Each of the repeaters, in at least the suboiiice, comprises a timing means including a stepping switch which is operative after a iirst time interval to cause warning current to be applied to an established communication connection set up by way of the associated trunk line between the suboiiice and the central office, and which is subsequently operative after a second time interval to cause the communication connection set up by way of the associated trunk line between the suboiice and the central oilice to be blocked.

In accordance with one feature of the invention the telephone system comprises rst and second exchanges, a trunk line including a first portion extending to the iirst exchange and a second portion extending to the second exchange, means including a reactance element reactively coupled between the portions of the trunk line for establishing a two-way communication connection between the portions of the trunk line,- and means in each of the exchanges for routing a connection by way of the trunk line to the other of the exchanges. Also the `telephone system includes a source of warning current, a control switch operative to change the reactive coupling of the reactance element between the portions of the trunk line, thereby to block the communication connection between the portions of the trunk line, and timing means for connecting the source of warning current to a connection routed by way of the trunk line between the exchanges a first predetermined time interval after the connection is routed therebetween and for automatically operating the control switch a second predetermined time interval after the connection is routed between the exchanges.

In accordance with another feature of the invention, there is provided in each of the exchanges an automatic switch having access to the trunk line extending between the exchanges, means including the automatic switches and the trunk line for setting up a two-way communication connection between the exchanges, control means for operating and for releasing the switches, and means operative to block a communication connection set up between the exchanges without releasing the automatic switches, whereby the automatic switches may be released under the control oi the control means. Furthermore, the system includes timing means for automatically operating the blocking means a predetermined time interval after a communication connection is set up between the exchange.

In accordance with another feature of the invention, there is provided in the system a repeater in the second exchange connected to the trunk line extending between the exchanges, a control trunk in the second exchange associated with the repeater, and an automatic switch in the second exchange having access to a line terminating at the second exchange and to the control trunk. A two-way communication connection between the first exchange and the lastmentioned line is set up by way of the trunk line, the repeater, the control trunk, and the automatic switch. The system also includes means responsive to received impulses projected over the trunk line to the second exchange for operating the repeater, first control means responsive to the operation of the repeater for causing the automatic switch to seize the control trunk, and second control means governed by the repeater for causing the automatic switch to seize the lastmentioned line, thereby to extend a call from the first exchange to the last-mentioned line. Furthermore, the system comprises a timer included in the repeater, means responsive to the operation of the repeater for initiating a timing operation of the timer, further control means Ogoverned by the completion of the timing operation of the timer for releasing the repeater, and means responsive to the answering of the call on the last-mentioned line for terminating the timing operation of the timer.

In accordance with a further feature of the invention, the telephone system comprises a plurality of subscriber lines, a switching link operative to set up connections between the lines, rst control means for causing the link to seize a calling one of the lines, second control means for causing the link to seize a called one of the lines, a number of characteristic sources of ringing current, means including a switch for selectively connecting the sources of ringing current to a called line, and means governed by the second control means for controlling the switch. Also the system comprises a source of warning current and timing means included in the switch for connecting the source of warning current to a connection established between two of the lines a predetermined time interval after the connection is set upv by way of the link.

In accordance with a further feature of the invention, the system comprises timing means including the switch for connecting the source of warning current to a connection established between two of the lines a iirst predetermined time interval after the connection is set up by Way of the link and for automatically releasing the link a second predetermined time interval after the connection is set up `by way of the link.

In accordance with a further feature of the amate V invention, the system'comprises a plurality of subscriber lines each including two line conductors, a number of ringing conductors individually connected to characteristic sources of ringing current, and a switch operative simultaneously to select either one of the line conductors of a called line and any one oi the ringing conductors. Furthermore, the system comprises timing means including the switch for connecting the vsource of warning current to an established connection between two of the lines a rst predetermined time interval after the connection is set up by way of the link and for automatically releasing the link a second predetermined time interval after the connection is set up by way of the link. A

Further features of the invention pertain to the particular arrangement of the circuit elements thereof, whereby the above-outlined and additionalfeatures are attained. I

The novel features believed to be characteristic o'f the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof will best be understood by reference to the following specication taken in connection with the accompanying drawings in which Fig. 8 illustrates the general arrangement of a telephone system including an automatic central oiiice andan automatic suboice and incorporating the present invention; Figs. 1 to 7, inclusive. taken together, illustrate thedetails of a system having incorporated therein the features of the system, as briefly outlined above; and Fig. 9 illustrates the mode of combining Figs. 1 to '7, in-

elusive, of the drawings to form a. unied system.

Description of the apparatus incorporated in th telephone system Referring now more particularly to Fig. 8 of the drawings, the telephone system there illustrated comprises an automatic central oilice 698, an automatic suboice 50 and a first group of two-way trunk lines extending therebetween and terminating at the suboilice, each of the lines in the first group of trunk lines being individuallyv associated with an alternating current repeater in the subofce 50 and provided with a control trunk individual thereto. For example, the line 694 included in the first group of trunk lines is v More specifically, the suboiiice 50 has an ultimate capacity of one hundred lines, the first and second groups of trunk lines may each comprise ten lines, and the number of subscriber lines may comprise eighty lines. The number of lines included in the rst and second group of trunk lines is determined by the amount of traic vwhich the suboifce 50 is required to handle and usually satisfactory service may be rendered when each of these groups of trunk lines includes three lines. y

Also the automatic central oflice 698 comprises a number of alternating current repeaters individually associated with the lines in the :Erst

group-of trunk lines extending to the suboflice Aincluding the link 60 so, a number of subscriber lines terminating thereathaving subscriber substations lassociated -therewithfa plurality of links various connections between the lines and a. distributor for assigning idle'ones of the links to the use of calling ones of the lines in a predetermined order. the central office 698 are not shown and may be of any conventional form. However, it is preferable that these pieces of apparatus in the central omce- 698. are of the same form as the corresponding pieces of apparatus inthe subofce 50, described in detail hereinafter.

Each of the links may be identical to the link 60 which comprises a nder portion or switch IM and a connector portion or switch 200, each having access to each line in the system. Preferably, the links are arranged in first and second groups, each group being provided with a distributor individual thereto for assigning idle ones of the' links in the groupto the use of calling lines. The number of links included in each group is determined by the amount of tralc which the suboiiice 50 is required to handle and usually satisfactory service may be rendered when each of the two groups of links includes ve links. For example, the first group of links is provided with a distributor 100. Also the lines terminating at the suboflice 50 are arranged in first and second groups which are individually associated with corresponding ones of the distributors whereby calling lines in the ilrst group of lines are normally assigned for use idle ones of the links in the first group of links, and calling lines in the second group of lines are normally assigned for use idle ones of the links in the second group of links, thereby rendering it possible to extend simultaneously a call initiated on a line in each of the two groups of lines. Furthermore, the

vdistributors are so connected and arranged that a call initiated on a line in the first group of lines is assigned for .use an idle link in the second group of links, in the event that all of the links in the first group of links are busy; and a call initiated on a line in the second group of lines is assigned for use an idle link in the first group of links, in the event all of the links in the second group of links are busy;

'I'he subscriber lines terminating at the suboflice 50 may comprise private automatic branch exchange or P. A. B. X. trunk lines, private lines and party lines, the subscriber lines H5 and 315 being party lines, each serving a number of subscriber substations, respectively including the subscriber substations A, B and C, D. Each of with the subscriber line H5 and the altern-ating current repeaterllll being respectively indicated at |00 and| 500. Each of the line circuits includes a line relay, a cut-olf relay and a lock-out relay, these relays in the line circuit |00 being Vrespectively indicated in Fig. l at Rl55, RIGU and for setting up thev These pieces of apparatus included in finder switch as best shown in Fig. 1, comprises a bank of fixed contacts |02 arranged in ten vertical levels, each level including ten radially disposed contact sets, each terminating a line extending thereto, a wiper set associated with the contact bank |02 and carried by a carriage movable in both vertica-l and rotary directions, a row of fixed contacts |04 arranged in vertical alignment, each terminating a control conductor, and a contact wiper associated with the row of contacts |04 and carried by the movable carriage. Also this Strowger mechanism includes a vertical magnet M|05 for moving the carriage in the vertical direction, a rotary magnet M|06 for moving the carriage in the rotary direction, and a release magnet MI01 for releasing the carriage and returning it to its normal position. Also associated with this Strowger mechanism are a s'et of switch springs |08, which are actuated by the movement of the carriage in a vertical direction away from its normal position, and a set of switch springs |09 which are actuated by the movement of the carriage into the eleventh radial position. Also the finder switch |0| comprises a switching relay R|80 and a control relay R|90.

The Strowger mechanism' included in the connector switch 200, Ias best shown in Figs. 2 and 3, comprises a bank of fixed contacts 300 arranged'in ten vertical levels, each level including ten radially disposed contacts sets, each terminating a line extending thereto, and a wiper set associated with the contact bank 300 and carried by a carriage movable in both vertical and rotary directions. Also this Strowger mechanism includes a vertical magnet M20I for moving the carriage in the vertical direction, a rotary magnet M346 for moving the carriage in the rotary direction, and a release magnet M344 for releasing the carriage and returning it to its normal position. Also associated with this Strowger mechanism are two sets of switch springs 209 and 345 whichare actuated by the movement of the carriage in the vertical direction away from the normal position, two sets of switch springs 2|0 and 338 which are actuated by the movement of the carriage in a vertical direction to the level of contacts in the contact bank 300 terminating the lines in the second group of trunk lines, and a set of switch springs 249 which are actuated by the movement of the carriage in the vertical direction to the level of contacts in the contact bank 300 terminating the lines in the first group of trunk lines. It is noted that the rst group of trunk lines terminate in the tenth level of contacts in the contact bank '.300 of this Strowger mechanism; the second group of trunk lines terminate in the'ninth level of contacts in the contact bank 300 of thismechanism; and the subscriber lines terminate in the first to the eighth, inclusive, levels of contacts in the contact bank 300 of this mechanism. Furthermore, it is noted that the Strowger mechanism included in the connector switch 200 is of the automatic trunk hunting type; viz., an idle line in the first group of trunk lines is seized 'thereby when the single digit 0 is dialed into the connector switch 200, and an idle line in the second Agroup of trunk lines is seized thereby when the first digit 9 followed by a predetermined second digit is dialed into the connector switch 200. Also a particular subscriber line is seized and rung by the connector switch 200 when the three digits corresponding to the directory number of the patricular subscriber line are successively dialed into the connector switch, regardless of whether the particular subscriber line ,is the calling subscriber line, which is seized on la reverting call, or an independent subscriber line. In calling a particular subscriber line, the first and second digits dialed into the connector switch 200 correspond to the position of the subscriber line in the contact bank 300 of the'Strowger mechanism included therein, while the third digit dialed into the connector switch determines the character of the ringing current to be projected over the seized line and the type of ringing circuit to be used, as is more fully explained subsequently.

The connector switch 200 also comprises a minor switch 325 which includes three rotary switches 326, 330 and 334, each including a con` tact bank and an associated wiper, the contact banks of these switches being indicated, respectively, at 329, 333 and 331, and the associated wipers thereof being indicated, respectively, at 321, 33| and 335. rI'he minor switch 325 also includes 'a rotary magnet M345 for driving the wipers of the rotary switches and a release magnet M343 for releasing the minor switch so that the wipers of the rotary switches may be automatically returned to their normal positions. Also associated with the'minor switch 325 is a set of switch springs 339 which are actuated by the movement of the wipers of the rotary switches thereof away from their normal `position. The minor switch 325 is utilized to select the particular frequency or code of the ringing current, depending upon whether harmonic or code ringing is employed in the system, to be projected over a line seized by the connector switch 200 and to select the particular conductor over which the ringing current is to be projected in the event a divided ringing circuit is employed in the system. Certain alternative wiring is provided including the wiring illustrated at X and Y in Fig. 3, which is connected in a manner more fully described subsequently in order to accommodate the use of the connector switch 200 to different types of ringing employed in the system. More particularly, the X" wiring is utilized when code ringing is employed in the system and comprises a connection between the ring pick-up lead C822 and the front contact associated with the armature RA399 of the switching relay R395. On the other hand, the Y wiring is utilized when harmonic ringing is employed in the system and comprises a connection between ground potential and the front contact associated with the armature RA399 of the switching relay R395.

Furthermore, the connector switch 200 comprises a group of relays and their control and controlled circuits, this group of relays including a line relay R260, a hold relay R265, a cutthrough relay R240, a. battery reversing relay l R250, a ring cut-off relay R360, a test relay R310,

a ring control relay R390, a switching relay R395, and a number of control relays R2l0, R220,

R225, R230, R210, R280, R345, R350, R355, R380 and R305.

A first timing arrangement is incorporated in the connector switch 200 which causes the connector switch to be released and a calling line associated therewith to be locked out, in the event the'connector switch isnot completely operated toselect a line terminating thereat, after it has bgen seized by the calling line. A second timing arrangement is incorporated in the connector switch 200 which is operative t warn the subscribers that an established connection including the subscribers substations has been held a predetermined time interval, and then to release automatically the established connection and to lock the calling and called lines out in ,the event the established connection is held an additional time interval.

A signaling arrangement is incorporated in the connector switch 200 which is operative to actuate an alarm in the event that `either the Strowger mechanism or the minor switch in-I cluded therein fails to restore completely after it has been released.

Preferably, each of the distributors isS con,

netted and arranged in a manner similar to that of the distributor 100 individually associated with the first group of links which comprises, as best shown in Fig. 7, a rotary switch 10| including four banks of fixed contacts and four wipers individually associated therewith, the corresponding contacts in each bank terminating the control conductors extending to the respective links in the rst group of links and the wipers terminating the control conductors extending to the distributor. Also the rotary switch 10| includes a rotary magnet M10I for driving the wipers associated with the contact banks. The distributor 100 also comprises a start relay R120, a switch-over relay R1I0, a test relay R130, a number of control relays R1I5, R135, R140, R150, R155Y and R160, and the control and controlled circuits therefor.

Also associated with the distributor 1.00 are av signal lamp 122, which is illuminated in the event the nder switch of the link assigned by the distributor to the use of a calling line does not nd the calling line Within a predetermined time interval, and a signal lamp 123 which is illuminated in the event that the carriage of the Strowger mechanism included in the finder switch of a link employed in an established connection does not restore to its normal position incident to the release of the established connection. A counting meter M124 is associated with the distributor 100 in order to count the number of calls which are extended by way of the links in the first group of links associated with this distributor.

The distributor 100 is so connected and arranged that a second idle link in the rst group of links is assigned to the use of a calling line in the iirst group of lines, in the event that a irst idle link in this group assigned thereto fails to iind the calling line during the course of operation thereof. Also a testing arrangement comprisinga switch 182 is provided in the distributor 100 in order to provide for automatic testing of the finder switch of each link in the rst group of links.

The distributor 100 is of the preselective type in that an idle link in the rst group of links isV selected to be assigned to the use of a calling line in the first group of lines prior to the initiation of a call on a line therein, and another idle link in the first group of links is automatically selected Yto be assigned to the use of the next calling line in the first group of` lines as soon as the selected link operates to lnd a calling line in the rst group of lines. "Also, the distributor 100 is so connected and arranged that when all of the links in the ilrst group of links are busy the start circuit ofthe distributor 100 is transferred to the distributor associated with the second group of lines, whereby the secondmentioned distributor assigns idle ones .of the links in the second group of links to the use of the calling linesin the rst group of lines.

Preferably, each of the alternating current repeaters is connected and arranged in a anner similar to that of the alternating current repeater 400 which comprises, as best shown in Figs. 4 to 6, inclusive, a transformer 600,- a control trunk I 30 having a line circuit 500 individual thereto, and a minor switch 625 including two rotary switches SI5 and 6I8. Also the .minor switch 625 includes a. rotary magnet M6|2 for driving the wipers thereof,` and a release magnet M6I3 for returning the wipers thereof to their normal positions. The minor switch 625 comprises 'a portion of an arrangement for warning the subscribers holding an established connection including the repeater 400 that the established connection has been Iheld iorfa predetermined time interval and then for automatically interrupting the established` connection including the repeater 400 after an additional time interval.

The repeater 400 also comprises a line relay R405, a battery reversing relay R4 I 0, two impulse relays R420 and R680, a timer start relay R450, two switching relays R460 and R550, an answer relay R565, a ring-up relay R630, a group of control relays R425, R430, R435, R440, R445, R455, R505, R5I0, R5I5, R520, R525, R530, R535, R540, R560, R625, R635, R640, R645, R650 and R610, the control and controlled circuits therefor, and three impedance elements Z403, Z503 and Z655. In addition to the two-Way trunk line 694, two incoming trunk lines 320 and 486 are associated with the repeater 400, the line 320 being employed when battery reversing supervision on the calling line is utilized and the line 486 being employed when this type of supervision is not utilized.

Ordinary substation to substation calls within the suboce i An ordinary call which is to be extended from one subscriber substation to another within the suboce is initiated at the calling substation'by removing the receiver of the telephone instrument thereat from its hook. For exampleyfinextending a call from the subscriber substation A to the subscriber substation C within the subolce 50, the call is first initiated at the substation A by removing the receiver of the telephone instru' ment thereat from its hook, thereby to complete a bridge path at the telephone instrument at the substation A between the line conductors CHE and C I I1 of the subscriber vline II5 extending to the substation A. When this bridge path is completed between the line'conductors of the subscriber line M5 a circuit is completed for energizing the line relay RI55 in the line circuit I 00 individually associated with the subscriber line II5, which extends from battery at the upper winding of RI55 by way of the upper winding of RI55,.RAI62, Cl I6, the bridge path between CI I6 and CI I1, Cl I1, RAI63, and the lower winding of RI55 to ground. When energized over the above-traced circuit the line relay RI55 operates to complete, at RAI56, an obvious path for applying direct ground potential to the control conductor CI I9 of thesubscriber line II5 extending from the connector switches of the links having access thereto, thereby to mark the subscriber line |I5 as busy to the connector switches. Also the line relay R|55 completes, at RA|50, a path for applying ground potential to the conductor C|35, thereby to mark with ground potential in the contact banks of the Strowger mechanisms included in the finder switches of the first group of links, the level in which the subscriber line ||5 is terminated, and for applying ground potential to the start lead C|31 extending to the distributor 100 individually associated -with the first group of links. The path for marking the level in the contact bank |04 of the Strowger mechanism included in the finder switch |0| of the link illustrated extends from ground, at RAISB, by way of RAI 53 and the back contact associated therewith, C|35 and Cl35' to the contact |04' in the contact bank |04. The path` for applying ground potential to the start lead CI31,Aextend ing tothe distributor 100, extends from ground, at RAISE, by way of RAI53 and the back contact associated therewith, Cl35, and the resistor |95 to the start conductor` CI 31. It is noted that the contact |04' is the iirst contact in the contact bank |04 of the Strowger mechanism included in the nder switch IOI. Accordingly, the subscriber line I|5 is terminated in the rst level in the contact banks of the Strowger mechanisms included in the iinder switches of the rst group of links. Also, upon operating, the line relay RI55 completes, at RAI51, a path for applying battery potential to the control conductor CI I3 of the subscriber line II5, thereby to mark the radial position of the contact sets in the contact banks of the Strowger mechanisms included in the finder switches of the links terminating the subscriber line I|5. This path for applying battery potentialto the control conductor Cl I8 extends from battery at the winding of the cut-off relay RI60 by way of the winding of RI50, RAISI, andRAI51 to C|I8. l

This application of ground potential to the start lead C|31 extending to the distributor 100 completes a circuit for energizing the start relay R120, which extends from the grounded start lead C|31 by way of RA1I3 and the front contact associated therewith, and the winding of R120 to battery. When energized over the above-traced circuit the start relay R120 operates to initiate operation of the distributor 100, thereby to cause the idle one of the links in the first group, previously selected by the distributor 100, to be assigned to the use of the calling subscriber line H5. More particularly, upon operating, the Astart relay R120 prepares, at RA12I,

a circuit for illuminating the signal lamp 122, which circuit is completed by apparatus, not shown, in the event the start relay R120 remains operated for a predetermined time interval iindicating that the calling subscriber line ||5 has not been seized by the finder switch of a link in the rst group of links within a predetermined time interval. Also the start relay R120 completes, at RA120, a circuit for energizing the rotary magnet M10| of the rotary switch 10| in series with the relay R140, this circuit extending from ground, at RA158, by way of RA132, RA120, the winding of R140, RA1II, the selfinterrupting contact MA10| of the rotary magnet M10I, and the winding of M10| to battery. When the above-traced series circuit is completed the r rotary magnet M10| does not operate due to the high series resistance of the winding of the relay R140. However, the relay R140 operates. Upon operating, the relay R140 prepares, at RA141, a holding circuit, traced hereinafter, for

energizing the winding thereof and completes, at RA143, a path Afor applying ground potential to the control conductor C140, thereby to initiate operation of the iinder switch ofthe previously4 selected idle link in the first group. Assuming that the illustrated link 50 in the flrst group of links is the idle link previously selected by the distributor 100, this application of ground potential to the control conductor C140 completes a circuit for energizing the relay RI30 in the finder switch |0| of this link, this circuit extending from the grounded control conductor C140 by way of the wiper 104 and the associated contact 103m the rotary switch 10|, the conductor CI44, and the winding of RI90 to battery.

-Also the relay R140 prepares, at RA142 and the front contact associated therewith, a circuit, traced hereinafter, for energizing the rotary magnet M10| of the rotary switch 10|, and completes, at RA14I, a holding circuit for energizing the relay R1|0, the latter circuit extending from' ground, at RA14I, by way of C162 and the winding of R1|0 to battery. 'I'his holding circuit for the relay R1|0 retains this relay in its operated position during the operation of the distributor 100, thereby to prevent the relay R1I0 from re-l storing in the event that the link 60 is the last idle link in the first group of links. Also, upon operating, the relay R140 completes, at RA145, an obvious circuit for energizing the relay R150, prepares, at RA144, a circuit traced hereinafter for energizing the vertical magnet M|05 of the Strowger mechanism included in the nder switch |0I, and prepares, at RA145, a circuit traced hereinafter for energizing the upper winding of the test relay R130.

When energized the relay R150 operates to complete, at RA15I, the holding circuit for energizing the relay R140, this circuit extending from ground, at RA15|, by way of RA141, the winding of R140, RA1||, the self-interrupting contacts MA10I of the rotary magnet M10I, and the winding of M10| to battery. Also the relay R150 prepares, at RA15I, a holding circuit for energizing the lower winding of the test relay R130, and setsI its own weighted armature RA152 into vibration, thereby to complete intermittently, at RA152, the circuit for energizing the lower winding of the relay R155, this circuit extending,

'when completed, from ground, at RA152, by way due to this characteristic and the fact that lthe circuit for energizing the lower winding thereof is only intermittently completed, at`RA152 and WA152. v

When energized over the previously traced circuit the relay R| in the nder switch |0| operates to interrupt, at RA|94 and the back contact associated therewith, `the path for applying ground potential in the finder switch I0| to the all trunks busy conductor C|42. VAt this time multiple ground potential in the remaining idle links in the first group of links is applied to the all trunks busy conductor CM2, thereby to retain the relay R1|0 in its operated position subsequent to the restoration of the relay R to interrupt, at RA14I, the'holding circuit of the relay R1|0. Also the relay R|90 completes, at RA|04 and the front contact associated therewith, an obvlous'path for applying ground potential to the control conductor C|23 extending from the finder switch I0| into the aociated connector switch 200. This application of ground po- 2,214,256 v tential to the control conductor C|23 also. prepares a circuit traced hereinafter for energizing the lower winding of the relay RI00. Further the relay RISU interrupts, at RAI93 and the back contact associated therewith, the connection between the control conductor C`I23 and the guard conductor C14I, thereby to prevent the operation of the rotary lmagnet M10| of the rotary switch 10| in the distributor 100 prior to the operation of the iinder switch IUI to seize the calling subscriber line H5, this connection between the control conductor CI23 and the guard conductor C14|, prior to interruption, extending from the control conductor CI 23 by way of' the switch springs III and IIU of the vertical olf-normal springs |08, RAI93 and the back contact associated therewith, and CI43 to the guard conducc tor 014|. `Further the relay RI90 prepares, at RAI 92, and at RAI93 and the iront contact associated therewith, a circuit traced hereinafter for energizing the rotary magnet M'IUI of the rotary switch 10| in the distributor 100 subsequent to the operation of the nder switch IUI to seize the calling subscriber line I I5, and prepares, at RAI 92, a circuit traced hereinafter for energizing the rotary magnet MIUS'of the Strowger mechanism included in the finder switch IUI. Finally the relay R|90 completes, at RAIUI, a circuit for energizing the vertical magnet MIU5 of the Strowger mechanism included in the finder switch IUI, this circuit extending from ground, at RA158, by way of RA144, RA16I,v RA13I and the back contact associated therewith, C142, the wiper 105 and associated contact 109 of the rotary switch 10|, CI45, RAISI, and the winding of MIU5 to battery.

When energized over the above-traced circuit the vertical magnet MI 05 operates to move the carriage of the Strowger mechanism included in the nder switch I| one step in the vertical direction, and to complete, at MAI 05, a circuit for energizing the relay R160, this circuit extending from ground, at MAI05, by way of CI46, and the winding of R160 to battery. Also, at MAI U5, the vertical magnet MIU prepares a circuit or short-circuiting the upper winding of the test relay R130, this circuit extending, when completed, from ground, at MAI 05, by way of C|46, RA145, the upper winding of R130, RA133 and the back contact associated therewith, C143, the wiper 102 and'associated contact '|06 of the rotary switch C|40, and the control wiper to the associated grounded contact in the row of contacts |04 in the contact bank of the Strowger mechanism included in the finder switch IUI. When the carriage of the Strowger mechanism includedin the finder switch IUI is moved one step in the vertical direction, the vertical off-normal springs |08 associated therewith are actuated, thereby to prepare, at the switch springs |I3 and ||2 thereof, a circuit traced hereinafter for energizing the release magnet MIU1 of the Strowger mechanism included in the finder switch IUI, and to prepare, at the contact springs IIU and ||0' thereof, a circuit traced hereinafter for energizing the rotary magnet M10| of the rotary switch 10| by way of the guard conductor C14I. When energized overthe above-traced circuit the relay R160 operates to interrupt, at RA16I, the previously traced circuit for energizing the vertical magnet MIU5 of the Strowger mechanism included in the iinder switch 'IUI.

The vertical magnet MIU5 then restores to inter` rupt, at MAIU5, the previously traced circuit for energizing the relay R160 and the previously traced prepared path for short-circuiting the per winding of the relay R130. The relay R160 then restores to recomplete, at RA16I, the previously traced circuit for energizing the vertical magnet MIU5 of the Strowger mechanism included in the finder switch IUI. The vertical magnet MIU5 and the relay R160 continue, to interact, as described above, until the carriage of `the Strowger mechanismA included in the finder switch IUI is moved in a vertical direction to the level in which the calling subscriber line is terminated. In the present instance the calling subscriber line |15 is terminated in the first level. Accordinglyythevertical magnet MIU5 of the Strowger mechanism included in the finder switch IUI .is energized only once, thereby to cause the carriage of the Strowger mechanism to be moved in the vertical direction only one step,

at which time the control wiper carried thereby engages the contact |04' in the row of contacts |04 in the contact bank of the Strowger mechanism, thereby to complete a circuit for energizing the upper Winding of the test relay R130 in series with the winding of the relay R160. This circuit extends from ground, at yRAI58, by way of RAI 53 and the back contact associated therewith, C|35, CI35', the contact |04', the control wiper associated therewith, CI40, the wiper 102 and associated contact 106 of the rotary switch 10|, C143, RA133 and the back contact associated therewith, the upper winding of R130, RA145, and the winding of R160 to battery. During the pulsing of the vertical magnet MIU5 of the Strowger mechanism included in the finder switch IUI, the relay R155 does not operate due to its slow-to-operate characteristic and to the fact that the circuit for energizing the lower winding thereof is only intermittently completed, at RA152 and WA152. When energized over the above-traced circuit the relay R160 remains operated, and the relay R130 partially operates to close its X contacts associated with its armature RA133', thereby to complete a holding circuit for energizing the lower winding of R130, this circuit extending from ground, at RA15I by way of RA133', and the lower winding of R130 to battery. When this holding circuit is completed, the relay R130 completely operates to interrupt, at RA132, the original circuit for energizing the relay R140, and interrupts, at RA133 and the back contact associated therewith, the circuit for energizing the relay R160, thereby to cause the latter relay to restore. Also the relay R130 prepares, at RA133 and the front contact associated therewith, a circuit traced hereinafter for energizing the upper winding of the switching relay RI80. Further the relay R130 interrupts, at RA13| and the back contact associated therewith, la. point in the circuit for energizing the vertical magnet MI 05 of the Strowger mechanism included in the finder switch IUI, thereby to prevent further vertical movement of the carriage of this Strowger mechanism, and completes,- at RA13| and the front contact associated therewith, a circuit for energizing the rotary magnet MI06 of the Strowger mechanism included in the nder switch IUI subsequent to the restoration of the relay R160, the latter circuit extending from ground, at RA150, by way of RA144, RA16I, RA13| and the front contact associated therewith, CI4I, RAIS2, RA|84 and the back contact associated therewith, and the winding of MI06 to battery. Also the relay R130 completes, at RA133', a circuit for energizing the relay R135,

this circuit extending from ground, at RA15I, 75

per winding of R155 to battery. As the field produced by the upper winding of the relay R155 is in opposition to that originally produced by the lower winding thereof, and the facts that the relay R155 is of the slow-to-operate type and the circuit for energizing the upper winding thereof is only intermittently completed, at RA136 and WA136, operationof this relay is further delayed.

When the rotary magnet M106 of the Strowger mechanism included in the finder switch 101 is energized over the previously traced circuit, it operates to rotate the carriage thereof one step in the radial direction, vand to complete, at MA106, a circuit for energizing the relay R160, this circuit extending from ground,'at MA106, by way of C146, and the winding of R160 to battery. The relay R160 then operates to interrupt, at RA161, the circuit for energizing the rotary magnet M106, thereby to cause the rotary magnet MI06 to restore and interrupt, at MA106 the circuit for energizing the relay R160. The.

. relay R160 then restores'to complete, at RA161,

the circuit for energizing the rotary magnet M106, thereby to cause the rotary magnet M106 to operate and rotate the carriage of the Strowger mechanism included in the finder switch 101 a further step in the radial direction, andI to complete, at MA106,. the circuit for energizing the relay R160. The rotary magnet M106 and the relay R160 continue to interact, as described above, thereby to cause. the carriage of the Strowger mechanism included in the nder switch 10| to be rotated step by step in the rotary direction until the wipers carried by the carriage thereof engage the contacts in the contact bank 102 of the Strowger mechanism terminating the calling subscriber line 1 15. previously noted the relay R155 is of the slow-to-operate type and does not operate during the pulsing of the rotary magnet M106.

When the wipers carried by the carriage of the Strowger mechanism included in the finder switch 101 engage the contacts in the contact bank 102 thereof terminating the calling subscriber line 115, a circuit is completed for energizing the upper winding of the switching relay R180, this circuit extending from ground, at RA1I134 and the front contact associated therewith', by way of C143, the wiper 102 and associated contact 106 of the rotary switch 101, C140, the upper winding of R180, the control conductor C126, the wiper carried by the carriage of the Strowger mechanism terminating this control conductor, the contact in the contact bank 102 terminating the control conductor C118 of the calling subscriber line 115, C118, RA151, RA151, and the winding of R160 to battery. When energized over the above-traced circuit the relay R180 operatesrto connect, at RA181 and at RA182, the conductors -C124 and C125,

respectively, to the conductors C121 and C122 of the trunk line extending between the finder switch 101 and the connector switch 200, thereby to connect the calling subscriber line 115 through to the connector switch 200, and tointerrupt, at

RAI and the back X contact associated therewith, a point in the circuit for energizing. the rotary magnet M106 in the Strowger mechanism included in the finder switch 101, thereby to prevent further operation of the rotary magnet M106. Also the relay R180 completes, at RA1 84 and the front contact associated therewith, a holding circuit for energizing the lower winding thereof in series with the winding of the rotary magnet M106, this 'circuit extending from the grounded control conductor C123 by way of the lower winding of R180, RA184 and the front the rotary magnet M106 is energized over the above-traced circuit it does not operate due to the high series resistance of the lower winding of the relay R180. Further the relay R160 completes, at RA183, an. obviousconnection between yfrom the grounded control conductor C126, C1 18,

RA151, RA151, and the Winding of R160v to battery. When energized over the above-traced circuit the cut-off relay R160 operates to complete, at, RA161, a holding circuit for itself extending from the grounded control conductor C118 by way of RA161, and the, winding of R160 to battery. Also the cut-off relay R160 interrupts, at RA162 and at RA163, points in the bridge path for energizing the line relay R155, thereby to free the subscriber line 115 of impedance elements, and to cause the line relay R155 to restore. Further thel cut-off relay R160 completes, at RA164 and the front contact associated therewith, a connection between the control conductor C118 and the paystation tone lead C141 in the event that the subscriber substation A is of the paystation type, this connection extending from the paystation tone lead C141 by way of the condenser 148, RA164 and the front contact associated therewith, and RA161 to the control con- 'ductor C118 of the subscriber line 115. kIn the event the subscriber substation A is of the paystation type, paystation tone current is projected over the control conductor C1 18 of the subscriber line 1 15 by way of the operated iinder switch 101 into the associated connector switch 200 for a purpose more fully described subsequently. Finally, the cut-off relay R160 completes, at RA165 and the front contact associated therewith, an obvious circuit for energizing the lockout relay R150. Upon restoring, the line relay R155 interrupts, at RA158, a point in the path for applying ground potential to the start lead C131 extending into the distributor 100, and in the path for applying marking ground potential to the conductor C135' terminated by the contact 104 in the contact bank 104 pf the Strowger mechanism included in the finder switch 10|. When thus energized, the lock-out relay R operates to interrupt, at RAI53 and the back contact associated therewith, a further point in the paths for applying ground potential to the start lead C131 and the conductor C135. Also, upon restoring, the relay R completes, at RA156 and the back contact associated therewith, a path for ing to the finder switch 101 to the control conductor C119 of the subscriber line 115 extending contact associated therewith, and the winding .l

'of the rotary magnet MI06 to battery. When to the contact banks of the Strowger mechanisms included in the connector switches of the links having access to the subscriber line IIE, thereby to mark this subscriber line as busy. The lastmentioned path extends from the grounded control conductor CI I0 by way of RAISI and RA|56 and the back contact associated therewith, to the control conductor CI I0.

Furthermore, upon operating, the relay R|80 completes, at RAI85, a circuit for energizing the rotary magnet M10I of the rotary switch 10| in the distributor 100, this circuit extending from ground, at RA158, by way of RA144, RA16I, RA13I, and the front contact associated therewith, CI4I, RAI92, RAI85, RA|93, and the front contact associated therewith, CI43, the wiper 103 and associated contact 101 of the rotary switch 10|, C14I, RA142 and the front contact associated therewith, and the winding of M10I to battery. Also, at RAI85, the relay R|80 completes a path for short-circuiting the relay R140, this path extending from ground, at RA15I, by way of RA141, the winding of R140, RA1II, the seliinterrupting contacts MA10I of' the rotary magnet M10I, RA142 and the front contact associated therewith, C14I, the wiper 103 and associated contact 101 of the rotary switch 10|, CI43, RAI93 and the front contact associated therewith, RA|85, RAIBZ, CI4I, RA13| and the front contact associated therewith, RA16I, and RA144 to ground, at RA158. When the relay R140 is thus short-circuited it restores to interrupt, at RA141, a point in its holding circuit; and when the rotary magnet M10I `is energized over the above-traced circuit it operates to interrupt, at MA10I, a point in the original circuit for energizing the relay R140.

At this time, if no other calls have been initiated in the group of subscriber lines including the subscriber line when ground potential is moved from the start lead CI31, the start relay R120 restores. Upon restoring, the relay R120 interrupts, at RA120, a further point in the original circuit for energizing the relay R140, ang. interrupts, at RA12I, a point in the prepared' circuit ior illuminating the signal lamp 122. Upon restoring, the relay R140 interrupts, at RA143, the circuit for energizing the relay RI90. However, the relay RI90, being of the slow-to-release type, does not restore immediately. Also, upon restoring, the relay R140 interrupts, at RA142 and the front contact associated therewith, a point in the previously traced circuit for energizing the rotary magnet MI of the rotary switch 10i, and prepares, at RA142 and the back contact associated therewith, an alternative circuit traced hereinafter for energizing the rotary magnet M10I of the rotary switch 10|. Further, the relay R140 interrupts, at RA146, the circuit for energizing `the relay R150, and interrupts, at RA'M I, the holding circuit for the switch over relay Rii. At this time the relay R1|0 remains operated only in the event there is an idle link in the rst group of links. 'Ihe relay R150 then restores to interrupt, at RA152 and WA152, a further point in the circuit for energizing the lower winding of the relay R155, and interrupts, at RA15I, the circuit for energizing the relay' R135, and the holding circuit for energizing the lower winding of the relay R130.

When the original circuit for energizing the rotary magnet M10I of the rotary switch 10| is interrupted at RA142 and the front contact associated therewith upon the restoration of the relay R140, the rotary magnet M10I restores in order todrive the wipers 102, 103, 104, and 105 of the rotary switch 10| one step and into engagement with the next set of contacts terminating the control conductors oi' the next link in the rst group of links. Upon restoring, the rotary magnet M10I also prepares, -at its self-interrupting contacts MA10I, a point in the original circuit for energizing the relay R140. 'Ihe test relay R130 then restores, thereby to interrupt, at RA133 and the front contact associated therewith. the path for applying ground potential to the test conductor C143, and to prepare, at RA133v and the back contact associated therewith. the original circuit for energizing the upper winding of the relay R130. Also, upon restoring, the relay R130 interrupts, at RA13I and the front contact associated therewith, a further point in the circuit for energizing the rotary magnet MI05 of the Strowger mechanism included in the ilnder switch IOI, and prepares, at RA13| and the back contact associated therewith, a point in the circuit for energizing the vertical magnet MI05 of this Strowger mechanism. After a predetermined timeinterval the relay RI 00 restores to interrupt, -at RAI9I, a further point in the circuit for energizing the vertical magnet M|05 oi the Strowger mechanism included in the nder switch IOI, to interrupt, at RAI92, a further point in the original circuit for energizing the rotary magnet MI06 oi.' this Strowger mechanism, and to interrupt, at RA|94 and the front contact associated therewith, the path for applying multiple ground potential to' the control conductor CI23, ground potential being applied to the control conductor CI23 at this time in the connector switch 200 associated with the iinder switch |0| in a manner more fully described subsequently. Finally, upon restoring, the relay R| prepares, at RAI94 and the back contact associated therewith, a point in a circuit traced hereinafter for energizing the release magnet MI01 of the Strowger mechanism included in the nder switch |0I, this circuit being interrupted at this time, at RAI86 of the operated relay R|80, and completes, at RAI93 and the back contact associated therewith, a path for applying ground potential to the guard conductor CI43, this path extending from ground atthe switch spring II 0' oi the vertical o-normal springs |08 associated with the Strowger mechanism included in the finder switch lill by way of the switch spring ||0 and RA|93 and the back contact associated therewith, to the guard conductor CI43, This application of ground potential to the guard conductor C|43 marks the iinder switch I0| of the link 60 as busy to the distributor 100.

At this time the wipers 102, 103, 104, and '|05 of the rotary switch 10| in the distributor 100 engagel the control conductors extending to the nder switch of the next link in the iirst group' of links, and if this link is busy, ground potential appears upon the guard conductor thereof, thereby to complete a path for applying ground potential to the guard conductor C14I. This application of ground potential to the guard conductor 014| completes a circuit for energizing the rotary magnet M10I of the rotary switch 10 I this circuit extending from the grounded guard conductor C14I, by way of RA142 and the back contact associated therewith, RA1II, the self-interrupting contacts MA10I of the rotary magnet M10I, and

the winding of M10I to battery. Also, this application of ground potential to the guard conductor C14| prepares a point in a path for shortcircuiting the winding of the relay R140, therebyv to prevent the latter relay from'operating upon operation of the relay R120 incident to the initiation of another call in the group of subscriber lines served by the distributor 100 prior to the operation of the distributor 100 to select an idle link in the first group of links for the use of a calling line. When energized over the abovetraced circuit the rotary magnet M10| operates to move the wipers noted of the rotary switch 10| into engagement with the contacts thereof terminating the control conductor of the next link in the first group of links. In the event this link is also busy, ground potential appears upon the guard conductor thereof, thereby to cause the rotary magnet M10I toagain operate, as described above. 'Ihe rotary magnet M10| continues to operate, as described above, until the wipers noted of the rotary switch 10| engage a contact set therein terminating the control conductors of a iinder switch of an idle link in the first group' of links, at which time the circuit for energizing the rotary magnet M10| is interrupted due to the absence of ground potential upon the guard conductor of the inder switch of this idle link. At this time the distributor 100 is, completely released and in condition to assign the selected idle linkin the first group of links to the use of a calling line when the next call is initiated on a line in the ilrst group of lines served by the distributor 100.

Should a call be initiated on a line in the first group of lines prior to the operation of the distributor -100 to select an idle link in the ilrst group of links, the start relay R120 operates, as previously explained. However, operation of the relay R120 at this time is ineffective to cause the relay R140 to operate as the latter relay remains short-circuited due to the presence of ground upon the guard conductor CNIi as previously noted, so long as the wipers of the rotary switch.

10| in the distributor 100 encounter contacts thereof terminating control conductors of ilnder switches associated with busy links in the first group of links.

As previously noted, upon the operation of the switching relay R|00 incident to the seizure of the calling subscriber line I I0 by the finder switch I0| of the link 00, the relay R140 is shortcircuited and restores. Upon restoring, the relay R140 interrupts, at RAN I, the holding circuit for the switch over relay R1I0, which latter relay is retained in its operated position only in the event that there are other idle links in the flrst group of links, due to the fact that ground potential is applied to the all trunks busy conductor CM2 only in the event there are other idle links in the ilrst group of links. y At this time, in the event all of the links in the iirst group of links are busy, the relay R1 I 0 restores. Upon restoring, the relay R1I0 interrupts, at RA1|0 and the front contact associated therewith, the connection between the start lead C|31 and the start relay R120, thereby to prevent the distributor 100 from being started into operation when the next call in the group of lines served thereby is initiated on one of these lines. Also, upon restoring, the relay R1I0 connects, at RA'III and the back contact associated therewith, the start lead CI31 to the conductor C105 extending to the distributor individually associated with the second group of lines, thereby rendering the last-mentioned disaaiaass the distributor individually associated with the second group of lines to assign a previously selected idle link in the second group of links to the use of a calling line in the-first group of lines is otherwise the same as the operation of the distributor 100, previously described.- Also, upon restoring, the relay R1I0 interrupts, at RA1| I, a point in the circuit for energizing the rotary magnet M10| by way of the guard conductor CNI, thereby to prevent unnecessary operation of the rotary magnet M10| when all of the links in the ilrst group of links are busy.

In the foregoing description of the operation of the finder switch III of the link 00 it was alsumed that the carriage of the Strowger mechanism included therein was rotated step by step until the wiper carried by the carriage thereof encountered the contact inthe contact bank |02 thereof terminating the control conductor CI I0 of the calling subscriber line H0, at which time the switching relay RI00 was operated to interrupt the circuit for energizing the rotary magnet MI of the Strowger mechanism included in the ilnder switch |0I, thereby to arrest further rotary movement of the carriage of this Strowger mechanism, and to connect the calling subscriber line through to the connector switch 200, as previously noted. However, should the wipers carried by the carriage of this Strowger mechanism fail to encounter the contact in the contact bank |02 terminating the control conductor CI I0 of the calling subscriber line III or to make imperfect contact therewith such that the switching relay R|00 fails to operate, the rotary magnet M|00 of this Strowger mechanism operates intermittently until the carriage thereof is moved into its eleventh radial position. When the carriage of this Strowger mechanism is rotated into the eleventh radial position the rotary switch springs |00 are moved into engagement, thereby to complete a path for applying ground potential to the ground conductor CI, this path extending from ground at the rotary switch springs |00 by way of RAI and the front4 contact associated therewith to the guard conductor Clll. This application of ground potential to the guard conductor CH3 completes the previously traced circuit for energizing the rotary magnet M1 of the rotary switch 10| in the distributor 100, thereby to cause the distributor 100 to operate to select the next idle link in the iirst group of links for the use of the calling subscriber line lli, in the manner previously explained. Thus it will be apparent that the distributor 1001s so connected and arranged that a second idle link in the ilrst group of links is automatically se-v lected for the use of a calling line in the event that the ilnder switch of a first selected -link in :he ilrst group of links fails to ilnd the calling ine.

Also it is noted that an arrangement is incorporated in the distributor 100 for locking this distributor out of service in the event that it fails to operate properly to cause the finder switch of an idle link in -the ilrst group of links selected, thereby to seize a calling subscriber line. For example, sho'uld either the vertical magnet M|00 or the rotary magnet MI of the Strowger mechanism included in the finder switch |0| of the link 60 fail to cause the relay R100 to transmit operating pulses to either one of these magnets, after a predetermined time interval the operated relay R1I0 or the operated relay R1I0 is eii'ective to cause the relay R1I0 to l to cause the relay R155 to operate. More particularly, in the event that the rotary magnet M|05 fails to operate or to cause the relay R160 to transmit pulses thereto, the operated relay R135 causes the circuit for energizing the upper winding of the relay R155 to be energized a time interval suiiiciently long to cause the relay R155 to operate. Upon operating, the relay R155 completes, at RA159, a circuit for energizing the relay R150 by way of the all trunks busy conductor C163 extending to the distributor individually associated with the second group of links, this circuit extending from the grounded all trunks .busy conductor C153 by way of the switch 180, RA159, and the winding of R150 to battery. Also the relay R155 completes, at RA151, a path for applying ground potential to the guard conductor C14|, this path extending from ground, at RA15I, by way of RA141 and RA151 to the guard conductor C141. This application of ground potential to the guard conductor C14| completes the previously traced circuit for energizing the rotary magnet M10| of the rotary switch 10| in the distributor 100, and completes the previously traced path for shortcircuiting the winding of the relay R140. The relay R140 then restores and interrupts, at RA142 and the front contact associated therewith, a point in the circuit for energizing the rotary magnet M10| of the rotary switch 10|, thereby to cause the rotary magnet M10| to restore and advance the wipers noted of the rotary switch 10| one step and into engagement with the contacts terminating the control conductors of the finder switch in the next link in the first group of links. Also the relay R140 interrupts, at RA14I, the holding circuit of the relay RHI);v

and the operated relay R155 interrupts, at RA156, a point in the circuit for energizing the relay R1|0 by way of the all trunks busy conductor CI42, thereby to cause the relay R1|0 to restore. Upon restoring, the relay R1|0 interrupts, at RA1| i, a point in the original circuit for energizing the relay R and a point in this circuit for energizing the rotary magnet-M10| of the rotary switch 10| in the distributor 100. Furthermore, the relay R1-|0 interrupts, at RA1|3 and the front contact associated therewith, a point in the circuit for energizingthe start relay R120 by way of the start lead Cl31, and completes, at RA1|3 and the back contact associated therewith, a connection between the start lead C|31 and the conductor C165 extending to the distributor associated with the second group of links. It is noted that the circuit for energizing the relay R is completed by way of the all trunks busy conductor C163 of the distributor associated with the second group of links and that the operated relay R150 retains completed the circuit for energizing the lower winding of the relay R155. In turn the operated relay R retains the circuit for energizing the relay R150 completed at RA159. Accordingly, the relays R150 and R155 remain in operated positions until the circuit for energizing the relay R150 is interrupted by manually operating the switch to its open position. Thus the distributor 100 associated with the rst to the guard conductor CI43.

group of links is permanently locked out of 'service until the switch 180 is manually operated.

Before continuing with the operation of the connector switch 200 associated with the finder switch lul. in the link so, it is noted that the' finder switches oi' the links in the rst group of links may be tested automatically and sequentially by operating the test switch 182 to its closed position. When the test switch 182 is thus Operated a circuit is completed'for energizing the start relay R120, this circuit extending from ground, at the test switch 182, by way of the resistor 18|, the start lead C|31, RA1|3 and the front contact associated therewith, and the winding of R120` to battery. When the start relay R120 is thus energized it operates to cause the distributor 100 to assign the previously selected link to the use of a calling line. Assuming that the iilustrated'link 60 is thelink previously selected by the distributor 100' to the use of the calling line, the distributor 100 then operates to cause the vertical magnet M|05 ot the Strowger mechanism included in the finder switch |0| to operate intermittently, thereby to move the carriage of this Strowger mechanism in the vertical direction. Assuming that no legitimate call is initiated on a line in the rst group of lines during the time interval the finder switches of the links in the first group of links are being tested, the carriage of the Strowger mechanism included in the finder switch 0| is moved vertically to the tenth level wherein the previously traced circuit for energizing the upper winding of the relay R130 is completed due to the fact that the tenth contact in the row ofvcontacts |04 in the contact bank of this Strowger mechanism is permanentlygrounded. The relay R130 then operates, as previously explained, thereby to cause the rotary magnet M|06 to be intermittently energized in order to drive the carriage of the Strowger mechanism included in the finder switch |0| step by step in a rotary direction'until this carriage is moved-into the eleventh radial position. When the carriage of the Strowger mechanism included in the finder switch |0| is movedinto the eleventh radial position, the rotary springs |09 are closed, therebyto cause ground potential to be applied This application of ground potential to the guard conductor C|43 causes the rotary magnet M10| of the rotary switch 10| to be energized, thereby to drive the wipers noted of the rotary switch 10| one step and into engagement with the contacts terminating the control conductors of the nder switch in the next idle link. The finder switch of the next idle link is then caused to operate in a manner similar to that described above. 'I'his operation of the-distributor 100 will continue aslong as the test switch 182 remains in a closed position, thereby to test sequentially the nder switches of the idle links in the rst group of lines.

In the event that a legitimate call is initiated on a line in the rst group of lines during the time interval that the iinder switches of the idle links in the first group of links are being tested, the wiper carried by the carriage of the Strowger mechanism included in an operating one of vthe finder switches' will engage the marked contact in the row of contacts corresponding to the row of contacts I 04 in the contact bank of this Strowger mechanism prior to the movement of the carriage of this Strowger mechanism in the vertical direction to the tenth level, thereby to cause this operating nder switch to seize the calling line. After this nder switch seizes the calling line, the distributor 100 continues to operate as previously described to test the remainder of the finder switches of the idle links in the ilrst group of links.

Continuing now with the operation of the connector switch 200 to extend the call from the subscriber substation A to the subscriber substation C, when the relay RI90 in the finder switch IOI operates to complete the previously traced path for applying ground potential to the control conductor CI23, a circuit for operating the relay R220 is completed, this circuit extending from ground, at RAISI and the front contact 'associated therewith, by way of the control conductor CI23, RA2I4, and the winding of R220 to battery. Also this application of ground potential to the control conductor CI23 completes a circuit for energizing the upper winding of the relay R210,

this circuit extending from the grounded control conductor CI23 by way of the vertical off-normal springs 209 associated with the Strowger mechanism included in the connector switch 200, and the upper winding of R210 to battery. When energized over the above-traced circuit the relay R210 operates to prepare, at RA21I and RA212, a circuit traced hereinafter for energizing the upper and lower windings of the line relay R260 by way of a loop circuit including the bridge at the substation A across the line conductors CI I6 and CI I1 of the calling subscriber line II5 subsequent to the operation of the finder switch IOI to seize the calling subscriber line II5.

After the nder switch IOI seizes the calling subscriber line H5, and the switching relay RI60 operates to connect the calling subscriber line I I6 to the trunk line |20, a loop circuit is completed for energizing the relay R260, this circuit extending from ground, at RA21I, by way of RA212, the lower winding of R260, RC2156, RA255, RC2, RA245, C203, RA2I2, CI22, RAI82, CI25, the wiper and contact in the Strowger mechanism included in the finder switch IOI, the bridge at the substation A between the line conductors CII1 and CII6 of the subscriber line II5, CII6, the contact and Wiper of the Strowger mechanism included in the nder switch IOI, Cl2l, RAIBI, Cl2l, RAZII, C202, RA242, RC2I3, RA252, RC253, and the upper winding of R260 to battery. When energized over the abovetraced circuit the relay R260 operates to complete, at RA26I and the front contact associated therewith, a circuit for energizing the hold relay R265, this circuit extending from ground, at RA241, by way of RA26I and the front contact associated therewith, and the winding of R265 to battery. When energized over the above-traced circuit the relay R265 operates to complete, at RA265 and the front contact associated therewith, a path for applying multiple ground potential to the control conductor CI23, this path extending from ground, at RC236, by way of RA235, C239, and RA265 and the front contact associated therewith, to CI23. It is noted that the relay R265 operates to apply multiple ground potential to the control conductor CI23 prior to the restoration of the relay RI90 in the finder switch IOI due to the slow-to-release characteristic of the latter relay. Also, upon operating, the relay R265 prepares, at RA269, a circuit for impulsing the control magnets of the Strowger mechanism and the minor switch 325 included in the connector switch 200, in a manner more fully described subsequently. Also, it is noted that the ground potential connected to RA21I is connected thereto by way of a dial tone conductor. Thus it will be apparent that dial tone current is returned to the substation A over the previously traced loop circuit extending thereto in order to actuate the receiver of the telephone instrument thereat, thereby to indicate to the subscriber at the substation A that a link has been seized and that the rst digit of the directory number of the called subscriber line may be dialed. Also the relay R265 completes, at RA266, an obvious circuit for energizing the relay R226, which latter relay operates to apply, at RA228, ground potential to the time start lead C229 for a purpose more fully described subsequently.

'I'he subscriber at the substation A then dials the first digit of the directory number of the called subscriber line at the dial mechanism thereat, thereby to transmit a rst series of impulses by way of the subscriber loop circuit to the line relay R260. The relay R260 follows the dialed impulses in the usual m-anner, restoring each time the loop circuit is interrupted, and

operating each time the loop circuit is completed.

Each time the relay R260 restores it' interrupts, at RA26I and the front contact associated therewith, the energizing circuit of the relay R265, and completes, at RA26I and the back contact associated therewith, a circuit for energizing in multiple the lower winding of the relay R210 and the vertical magnet M20I of the Strowger mechanism included in the connector switch 200. The lastmentioned circuit extends from ground, at RA241, by way of RA26I and the back contact associated therewith, and RA269 to RA214 and the front contact associated therewith, one branch oi' this circuit extending from the front contact associated with RA214 by way of the lower winding of R210 to battery, and the other branch extending from the front contact associated with RA214 'by way of the winding of the vertical magnet M20I to battery. The relays R265 and R210 are of the slow-to-release type. Thus, these relays remain operated during impulsing. Each time the vertical magnet M20I is energized the carriage of the Strowger mechanism included in the connector switch 200 is moved one step in the vertical direction. When the carriage of this Strowger mechanism is moved away from its normal position one step in the vertical direction, the vertical off-normal springs 209 and 345 are actuated. The vertical off-normal springs 209 are actuated to interrupt the circuit for energizing the upper winding of the relay R210, and the vertical oft-normal springs 345 are actuated to prepare a point in the circuit for energizing the release magnet M3 of this Strowger mechanism. At the conclusion of the first digit dialed the relay R260 reoperates, thereby to interrupt, at RA26I and the back contact associated therewith, the previously traced circuit for energizing in multiple the lower winding of the relay R210, and the winding of the vertical magnet M20l. When this circuit is interrupted further operation of the vertical magnet M20I is arrested, thereby to arrest the car- .riage of the Strowger mechanism included in the connector switch 200 in a vertical position corresponding to the tlrst digit dialed and to the level in the contact bank 300 of this Strowger mechanism in which are disposed the contacts terminating the conductors of the called subscriber line 3I5 extending to the substation C. Shortly after this circuit is interrupted the relay R210, being of the slow-to-release type, restores to interrupt, at RA21I and RA212, the circuit for re- 

